This invention relates to controlling gain for a microphone signal.
In telephony, audio signals (e.g. including voice signals) are transmitted between a near-end and a far-end. In a bidirectional voice communication, the “near-end” and “far-end” are defined relative to each participant. Thus, the “near-end” for one participant will correspond to the “far-end” for the other participant. Far-end signals which are received at the near-end may be outputted from a loudspeaker at the near-end. A microphone at the near-end may be used to capture a near-end signal to be transmitted to the far-end, such as a voice of a participant at the near-end.
The quality of the audio outputted by the far-end loudspeaker may be affected by the amount of gain that is applied to the signal captured by the near-end microphone. For example, if the signal captured by the microphone has a high volume (e.g., which may be due to near-field speech caused by a person talking very close to the microphone) and a high gain is applied to that signal, then this may lead to signal saturation and so a poor quality signal is sent to the far-end. Whereas, if the signal captured has a low volume (e.g., which may be due to far-field speech caused by the person talking being far away from the microphone) and a low gain is applied, then this may lead to a low signal-to-noise ratio (SNR). Furthermore, a speech signal may change from far-field to near-field (and vice versa) as a person speaking moves towards or away from the microphone. This will affect the power (or amplitude) of the speech signal that is incident at the microphone and so the amount of gain that is applied to the signal will need to be appropriately adapted and the adaptation should be performed in a timely manner so as to maintain the quality of the signal sent to the far-end. Furthermore, changing the amount of gain applied can cause a degradation in the performance of other signal processing modules at the near-end device such as automatic speech recognition (ASR), echo cancellation, noise cancellation and speech enhancement. There is, therefore, also a need to mitigate such degradation.